1.Multi-channel polarimetry has been performed to detect high rotation measure of 35 sources out of 96 radio source candidates. We found that there exist sources with RM of several thousands rad m^<-2>. Houever, We can not confirm a large rotation measure coused by high densities in CSS sources and in the culster of galaxies.2.Faraday rotations of the QSO's with strong absorption lines within the QSO itself are significantly higher than that of the QSO whose strong lines originated in the intervening gaseous halo of galaxies. The large rotation measure caused by high density gas and the magnetic field running parallel with the major axis of the radio sources.3.The observations of the polarization at 43 GHz show that the Galactic center arc region is highly polarized up to 50% and that the magnetic field are well ordered along the vertical filament. The large internal Faraday rotation (3000radm^<-2>) explaines the depolarization properties in the Galactic arc.4.We have observed the flux density and linear polarization at 3 cm for 93 core-dominated radio sources. Among them, 18 sources were classified as blazars and the remaining 67 sources are considered non-blazars. We conclude that the blazar and non-blazar sources form distinct classes ; that is, not all the core-dominated radio sources are blazars.